Conventionally, as to content distribution methods, following three approaches have been adopted especially for video distribution.
(1) A Method in which a User Selects a Distribution Rate
A method is being considered in which, an interface for setting a distribution rate which has an effect on QoE in the user side is prepared, so that the user sets a distribution rate considering the user's communication environment and the like. In many cases, three patterns of qualities of high/medium/low and the like are prepared for distribution rates. Currently, in video distribution services such as YouTube (registered trade mark), there is an interface by which image quality can be selected (refer to non-patent document 1).
(2) A Method in which a Content Distributor Side Selects a Distribution Rate
In this method, content distribution of quality of low rate is performed in a time zone in which the number of users of the content distribution service is large, and content distribution of higher quality of medium/high rate is performed in a time zone in which the number of users of a content distribution service is small. Accordingly, even in a congested time, it becomes possible to provide services by a quality that can minimally satisfy service users. Also, it becomes possible to provide a high quality service depending on the number of users and premium payment. Currently, in the nico nico video (registered trade mark), a measure is carried out to lower the distribution rate in a congested time for free members (refer to non-patent document 2).
(3) A Method for Selecting a Distribution Rate According to Communication Status
In this method, an available band of a user is estimated in some form, so that content is delivered by a bit rate according to the available band. This method is classified to some schemes with respect to the scheme for estimating the available band.
a. Passive Type Estimation Scheme
In the passive type estimation scheme, the available band is estimated from a past communication history and the like.
In this scheme, estimation is performed by utilizing some tendency on the available band. For example, estimation of the available band is performed by using stationarity of time series (refer to non-patent document 3).
b. Active Type Estimation Scheme
In the active type estimation scheme, short communication is performed before distribution, so that the available band is estimated based on communication performance at that time. For example, a packet group, called a packet train, that sequentially becomes large is transmitted before communication, and the available band is estimated based on a change amount of delay to arrival (refer to non-patent document 4).
c. Feedback Scheme
In the feedback scheme, in the middle of distribution, the speed of the communication itself is measured, so that the distribution rate is changed in real time in accordance with the communication speed at that time. This scheme is mainly applied to video distribution in which the distribution rate can be changed in the middle. In video distribution that incorporates this scheme, content is divided into files of a short time unit called a chunk type, network quality (NW quality) and the like is measured between a server and a client for each chunk, and a distribution rate of a chunk that the terminal receives next is determined based on the measurement result, so that the content is distributed. Accordingly, by storing content in a playback buffer of a user terminal and reproducing the content, high quality content distribution becomes available even in a low rate (refer to non-patent documents 5, 6)